Captain of a cessna citation III, C650, lost control of the aircraft after encountering moderate to severe turbulence when descending from FL370 for FL330 resulting in an altitude overshoot to FL290. ATC reclred to FL290 after flight crew reported the reason for the overshoot.

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Attributes
ACN	401360
Time
Date	199804
Day	Tue
Local Time Of Day	0601 To 1200
Place
Locale Reference	atc facility : jot
State Reference	IL
Altitude	msl bound lower : 29000 msl bound upper : 33000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	artcc : zau
Operator	general aviation : corporate
Make Model Name	Citation III, VI, VII
Operating Under FAR Part	Part 91
Navigation In Use	Other Other
Flight Phase	descent other
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 60 flight time total : 7000 flight time type : 40
ASRS Report	401360
Person 2
Affiliation	Other
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 30 flight time total : 20000 flight time type : 10
ASRS Report	401510
Events
Anomaly	altitude deviation : overshoot inflight encounter : weather non adherence : clearance other anomaly
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance flight crew : regained aircraft control
Consequence	Other
Supplementary
Primary Problem	Weather
Air Traffic Incident	Pilot Deviation

Narrative:

During cruise descent from FL370 to FL330 aircraft encountered moderate to severe turbulence at FL335-338. Aircraft continued an uncommanded descent to FL290 before being able to regain level flight. When aircraft control was regained ATC was notified and we were told to maintain FL290 and ATC was informed of turbulence. Pilot called FSS when on the ground at mke and was given a PIREP. Some turbulence was being reported in the area but not expected to be severe. ATC did not indicate there was any loss of separation and TCASII showed no loss of separation. This was my first encounter with severe turbulence and an altitude loss of this magnitude. The onset of conditions was immediate and totally unexpected and maintaining a wings level pitch level to slightly above was my primary consideration along with notifying ATC as soon as possible.

Original NASA ASRS Text

Title: CAPT OF A CESSNA CITATION III, C650, LOST CTL OF THE ACFT AFTER ENCOUNTERING MODERATE TO SEVERE TURB WHEN DSNDING FROM FL370 FOR FL330 RESULTING IN AN ALT OVERSHOOT TO FL290. ATC RECLRED TO FL290 AFTER FLC RPTED THE REASON FOR THE OVERSHOOT.

Narrative: DURING CRUISE DSCNT FROM FL370 TO FL330 ACFT ENCOUNTERED MODERATE TO SEVERE TURB AT FL335-338. ACFT CONTINUED AN UNCOMMANDED DSCNT TO FL290 BEFORE BEING ABLE TO REGAIN LEVEL FLT. WHEN ACFT CTL WAS REGAINED ATC WAS NOTIFIED AND WE WERE TOLD TO MAINTAIN FL290 AND ATC WAS INFORMED OF TURB. PLT CALLED FSS WHEN ON THE GND AT MKE AND WAS GIVEN A PIREP. SOME TURB WAS BEING RPTED IN THE AREA BUT NOT EXPECTED TO BE SEVERE. ATC DID NOT INDICATE THERE WAS ANY LOSS OF SEPARATION AND TCASII SHOWED NO LOSS OF SEPARATION. THIS WAS MY FIRST ENCOUNTER WITH SEVERE TURB AND AN ALT LOSS OF THIS MAGNITUDE. THE ONSET OF CONDITIONS WAS IMMEDIATE AND TOTALLY UNEXPECTED AND MAINTAINING A WINGS LEVEL PITCH LEVEL TO SLIGHTLY ABOVE WAS MY PRIMARY CONSIDERATION ALONG WITH NOTIFYING ATC AS SOON AS POSSIBLE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.